the corn earworm, Helicoverpa zea, is a major target pest of the insecticidal Vip3Aa protein used in pyramided transgenic Bt corn and cotton with Cry1 and Cry2 proteins in the U.S. The widespread resistance to Cry1 and Cry2 proteins in H. zea will challenge the long-term efficacy of Vip3Aa technology. Determining the frequency of resistant alleles to Vip3Aa in field populations of H. zea is critically important for resistance management. Here, we provided the first F 2 screen study to estimate the resistance allele frequency for Vip3Aa in H. zea populations in Texas, U.S. In 2019, 128 H. zea neonates per isofamily for a total of 114 F 2 families were screened with a diagnostic concentration of 3.0 μg/cm 2 of Vip3Aa39 protein in diet-overlay bioassays. The F 2 screen detected two families carrying a major Vip3Aa resistance allele. The estimated frequency of major resistance alleles against Vip3Aa39 in H. zea in texas from this study was 0.0065 with a 95% CI of 0.0014-0.0157. A Vip3Aa-resistant strain (RR) derived from the f 2 screen showed a high level of resistance to Vip3Aa39 protein, with a resistance ratio of >588.0fold relative to a susceptible population (SS) based on diet-overlay bioassays. We provide the first documentation of a major resistance allele conferring high levels of Vip3Aa resistance in a field-derived strain of H. zea in the U.S. Data generated from this study contribute to development of management strategies for the sustainable use of the Vip3Aa technology to control H. zea in the U.S. Genetically engineered crops producing insecticidal Cry and Vip proteins from the bacterium Bacillus thuringiensis (Bt) have been planted for control of insect pests for more than two decades 1. Field efficacy of these Bt crops has been outstanding in controlling most target species, resulting in substantial economic, environmental and social gains 2-7. However, with large scale adoption comes intense selection pressure for development of resistance and challenges for long-term sustainability 8,9. To date, field-evolved practical resistance to Bt crops has been globally reported in at least 21 cases 10-15. To delay insect resistance development, an insecticide resistance management (IRM) plan based on a "high-dose refuge" strategy has been implemented in the U.S 16. Monitoring for evolution of resistance in field populations of the target insect species is an essential component of this IRM plan to maintain sustainability of Bt crop technologies. The corn earworm/cotton bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), is a major target pest of both Bt cotton and Bt corn in North America. Control of lepidopteran pests is achieved by the adoption of corn hybrids producing combinations of Cry1Ab, Cry1F, Cry1A.105, Cry2Ab2 and Vip3Aa20 insecticidal Bt proteins, and Bt cotton varieties producing combinations of Cry1Ac, Cry1F, Cry1Ab, Cry2Ab, Cry2Ae, and Vip3Aa19 17 .